1. Field of the Invention
This invention relates generally to the field of demilitarizing chemical warfare agents. More particularly, the invention relates to demilitarizing the agent HT using biodegradation.
2. Description of the Prior Art
Various nerve and vesicant-type chemicals are highly toxic entities which may be employed as chemical warfare agents. The United States military has a relatively large amount of these agents in its chemical warfare agent stockpile. However due to several circumstances, the United States has found it desirable to decrease its inventory of these agents.
In the past, incineration provided a means to dispose of these agents. Incineration is, however, not without its drawbacks. For example, there is the potential for adverse repercussions if even a small amount of these agents is released via the incinerator emissions or spills during handling. Furthermore, due to its negative environmental impact, there has been an ongoing effort by the United States Army to find alternative technologies, when appropriate, to address these shortcomings.
HT is a mixture of about 60 wt % 2,2'-dichlorodiethyl sulfide ("HD" or "sulfur mustard") and about 40 wt % bis-(2-(2-chloroethylthio)ethyl) ether (T). The prior art has provided suggestions regarding the biodegradation of hydrolyzed HD (sulfur mustard). See Review and Evaluation of Alternative Chemical Disposal Technologies, National Research Council, National Academy Press, Washington, D.C., 1996, the contents of which are incorporated herein by reference. Biodegradation of the HT mixture, however, is not believed to have been previously disclosed.
The above-mentioned demilitarization of HD includes an initial hot water hydrolysis step which yields primarily thiodiglycol (TDG) and HCl. This initial hydrolysis step removes HD to undetectable (&lt;200 ppb) levels. The HCl is neutralized with NaOH to NaCl and water and the organic products are treated biologically in an aerobic Sequencing Batch Reactor (SBR) seeded with activated sludge. This process yields an aqueous effluent of very low aquatic toxicity (See Harvey, S. P., et al. HD Hydrolysis/Biodegration Toxicology and Kinetics, ERDEC-TR-382, December 1996, the contents of which are incorporated herein by reference), and contains about 2% salt (assuming a 1.3 weight % feed of hydrolyzed HD to the bioreactors). The final products of this process produced no observable dermal irritation or other toxic effects. The efficiency of organic carbon removal was greater than 90% and toxicity characteristic leachate protocol (TCLP) testing of the effluent detected no priority pollutants.
Although this method proved useful for HD, it was not clear that a similar method could be employed for HT due to the presence of the bis-(2-(2-chloroethylthio)ethyl) ether (T), which does not readily convert into TDG under the conditions which cause hydrolysis of HD. In short, the biodegradation properties of (T) alone or in combination with HD were unknown.